Magnetic printing base and method of making same

ABSTRACT

There is disclosed a magnetic printing base for one or more printing plates, a method of making the magnetic base, and a mold in which moldable, non-magnetic adhesive material is molded about various parts of the magnetic base. The base is structured to permit circuit devices and end plates to be interconnected by the non-magnetic material into a unitary arrangement. Each magnetic circuit device includes a flat magnet disposed between and in contact with a pair of flat magnetizable plates. The permanent magnets extend short of the final desired dimension of the base. The plates and the molded material initially extend beyond the final desired dimension of the base, but are trimmed off by a cutter to the final desired dimension after assembly of the base. To obviate the tendency of the printing plate to creep or drift, the spacing between the magnetic circuits is such that the strength, at surface of the base, of the magnetic flux field between next adjacent pole plates of adjacent magnetic circuit devices is equal to the strength, at the surface of the base, of the magnetic flux field between the pole plates of a magnetic circuit device itself.

United States Patent [191 Jenkins [4 1 May 27, 1975 I MAGNETIC PRINTING BASE AND METHOD OF MAKING SAME 22 Filed: Nov. 9, 1970 21 Appl. No.: 87,673

[52] US. Cl. 101/382 MV; 269/8; 29/D1G. 29; 29/428; 51/105 R [51] Int. Cl 1341f 27/00 [58] Field of Search 101/378, 382 R, 382 MV, 101/426; 269/8; 335/285, 286, 288, 296,

297, 301, 302, 306; 18/DIG. 62; 29/602,

607, 609, 629, DIG, 29, 428; 51/105 R [56] References Cited UNITED STATES PATENTS 1,531,492 3/1925 Marquardt 101/382 MV 2,178,774 11/1939 Bogoslowsky l8/DIG. 62 2,269,149 1/1942 Edgar 269/8 X 2,952,205 9/1960 Dunwoodie 101/378 2,996,791 8/1961 Hicks 29/609 X 3,039,389 6/1962 Meese et a1 101/378 3,097,598 7/1963 Hotop et a1 101/378 3,126,502 3/1964 Denis 335/306 X 3,180,259 4/1965 McKay 101/378 3,336,551 8/1967 Stead 269/8 X 3,352,000 11/1967 Altenburger... 29/609 X 3,496,866 2/1970 Nystrand 101/378 FOREIGN PATENTS OR APPLICATIONS 933,666 8/1963 United Kingdom 101/382 MV Primary Examiner-Edg21r S. Burr Assistant Examiner-E. H. Eickholt Attorney, Agent, or Firm-Joseph J. Grass 5 7 ABSTRACT There is disclosed a magnetic printing base for one or more printing plates, a method of making the magnetic base, and a mold in which moldable, nonmagnetic adhesive material is molded about various parts of the magnetic base. The base is structured to permit circuit devices and end plates to be interconnected by the non-magnetic material into a unitary arrangement. Each magnetic circuit device includes a flat magnet disposed between and in contact with a pair of flat magnetizable plates. The permanent magnets extend short of the final desired dimension of the base. The plates and the molded material initially extend beyond the final desired dimension of the base, but are trimmed off by a cutter to the final desired dimension after assembly of the base. To obviate the tendency of the printing plate to creep or drift, the spacing between the magnetic circuits is such that the strength, at surface of the base, of the magnetic flux field between next adjacent pole plates of adjacent magnetic circuit devices is equal to the strength, at the surface of the base, of the magnetic flux field between the pole plates of a magnetic circuit device itself.

18 Claims, 8 Drawing Figures SHEET l/VVE/VTOR WILLIAM A JENKINS BY 2 Z A TTORNE Y MAGNETIC PRINTING BASE AND METHOD OF MAKING SAME BACKGROUND OF THE INVENTION This invention relates to the art of magnetic printing bases, and methods of and molds for making same. There are numerous prior art patents relating to magnetic bases and the like; examples are US. Pat. Nos. 1,657,287, 2,481,191, 2,952,205, 2,992,733, 3,024,392, 3,027,835, 3,039,390, 3,086,461, 3,097,598, 3,180,259 and 3,509,819.

SUMMARY OF THE INVENTION The invention resides in a low-cost, unitized magnetic base especially adapted for holding a printing plate and in a method of for making such a magnetic base. Although the invention is illustrated in the form of a circular cylindrical roll, it is also applicable to a flat base of the type disclosed in above mentioned US. Pat. Nos. 2,481,191 and 3,027,835. The method of the inv'ention includes, in general, the steps of providing magnetic circuit means in the form of a fiat magnet disposed between and in contact with magnetizable plates, the magnet extending short of the final desired surface of the base and initially the plates extending beyond the final surface of the base. No attempt is made to size the plates exactly prior to assembly so long as they extend beyond the final surface of the base. Similarly, no attempt is made to size the magnets exactly so long as they extend short of the desired surface of the base. It is preferred to fill the space between adjacent plates around the magnet with moldable, non-magnetic adhesive material and to key the plates together. Spaces between the magnetic circuits are preferably also filled with the non-magnetic material. Keying is very simply effected by providing holes in the plates in a position so that at least a portion of each hole extends beyond the magnet, and in this manner the plates are keyed against rotation. Following the molding step, the partly finished base is trimmed off by turning it on a lathe in the case of a circular cylindrical base or by milling with a milling cutter in the case of a flat type base. An important feature of the invention is providing permanent magnets to create a constant strength magnetic flux field on the surface of the base by positioning the magnetic circuit devices so that irrespective of whether or not the printing plate (or plates) is as wide as the base and irrespective of the location of the plate on the base, the plate will be held in position without a tendency to creep or drift. One way of accomplishing that is to provide the magnetic circuit devices described above, to arrange the magnets so that alternate plates are poled north-south-north-south, and so on, and to space the magnetic circuit devices so that the strength of the magnetic flux field between next adjacent pole plates of adjacent magnetic circuit devices is equal to the strength of the magnetic flux field between the pole plates of a magnetic circuit device itself. The mold for making the base of the invention is economical to con struct having basically a pair of mold sections and end caps or plates. The mold sections have positioning means specifically in the form of grooves, formed at its inner surface. The end plates are clamped against the ends of the mold sections by means of tie rods which extend through the end plates externally of the mold sections.

BRIEF DESCRIPTION OF THE DRAWINGS FIG..1 is a perspective view of a magnetic base for printing plates;

FIG. 2 is a side elevational view, partly in section, of the magnetic base shown in FIG. 1;

FIG. 3 is a sectional view taken generally along line 3-3 of FIG. 2;

FIG. 4 is an enlarged fragmentary sectional view showing a portion of the magnetic base as it appears during one of the manufacturing steps;

FIG. 5 is an exploded perspective view of a mold in which the magnetic base can be molded;

FIG. 6 is a vertical sectional view of the mold, showing the magnetic base in the mold after the moldable material has filled the mold;

FIG. 7 is a sectional view taken generally along line 7-7 of FIG. 6; and

FIG. 8 is a sectional view taken generally along line 8-8 of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRE EMBODIMENT With particular reference to FIGS. 1, 2, and 3, there is shown a magnetic base in the form of a printing cylinder or drum generally indicated at 10 mounted on shaft 11. The base 10 can be secured to and driven by the shaft 11 or the base 10 can be rotatable with respect to the shaft 10 and driven by other means, as desired. The magnetic base 10 is illustrated as including a plurality of spaced apart permanent magnetic circuit devices generally indicated at 12. Each magnetic circuit device 12 includes a flat, annular, permanent magnet 13 and a pair of magnetizable pole plates 14. Each magnet has a central hole 13' and each plate 14 has a central hole 14'. A cylindrical mounting member 15 in the form of a sleeve is shown to pass through the holes 13 and 14' and forms a flux path for each of the magnetic circuits. The plates 14 and the member 15 are composed of magnetizable, easily machinable material such as low carbon steel. Endplates 16 are received about reduced portions 17 of the mounting member 15 at locations spaced apart from the endmost magnetic circuit devices 12. The magnetic circuit devices 12 are all constructed with equal strength; the magnets 13 are of the same size and composition and the pole plates 14 are of the same size and composition. The magnets 13 are so arranged that alternate pole plates 14 are poled north-south-north-south, and so on, in a direction longitudinally of the base 10 as indicated by N and S in FIG. 2. Accordingly, the next adjacent pole plates 14 of adjacent magnetic circuit devices 12 are of opposite polarity. In accordance with the invention, the distance between adjacent magnetic circuit devices 12 is not arbitrary, but rather it is established by spacing the magnetic circuit devices 12 apart by a distance at which the magnetic flux field strength between next adjacent pole plates 14 of adjacent magnetic circuit devices 12 are equal, or substantially so, to the magnetic flux field strength of the magnetic circuit devices 12 themselves. Once the spacing has been established for a magnetic base having circuit devices of a particular size, strength, material and configuration, any number of such bases can be constructed using the same spacing.

The external diameters of the magnets 13 are less than the external diameter of the base 10 whereas the plates 14 extend all the way to the final surface of the magnetic base 10. Each of the plates 14 has four equally spaced apart holes 18 near its periphery. The holes 18 extend at least partly beyond the associated magnets 13. The end plates 16 have four spaced apart apertures or holes 19 which are larger in diameter than the holes 18 in the plates 14. Moldable, non-magnetic, adhesive material 20, such as epoxy fills: the space between the magnets 13 and the surface of the base between associated plates 14, the spaces between the outer surface of the cylinder member 15 and the outer surface of the base between plates 14 of adjacent magnetic circuit devices 12, the spaces between the plates 14 of the endmost magnetic circuit devices and the associated end plates 16 between the cylindrical member 15 and the surface of the base 10, and the holes 18 and 19 in respective plates 18 and 19. The magnetic base 10 is accordingly formed into a unitary support structure in which a magnetizable printing plate or a printing plate having a magnetizable holding portion is held to the base 10 by magnetic attraction, and in addition, the plates 14 and the non-magnetic material 20 serve to provide a solid support for the printing plate or plates. To assure adequate keying of the material 20 to the member 15, the outer surface of the member 15 between the next adjacent plates 14 of adjacent magnetic circuit devices 12, and between the plates of endmost circuits 12and associated end plates 16 is roughened at. annular zones15. A fragmentary portion of one of these zones 15' is shown in FIG. 6. Roughening can be accomplished by knurling or any other suitable means.

With reference to FIGS. 1 and 3, printing plates P constructed at least in part of magnetizable material are shown held onto the base 10 by magnetic attraction. The base 10 is shown to be provided with four longitudinally extending slots or grooves 21 in its periphery. The slots 21 cut through the end plates 16, the non-magnetic material 20, and the plates 14. Leading edges of four of the printing plates are shown to be received in the grooves 21 which prevents the printing plates P from creeping around the base 10 as its rotates during the printing operation. The grooves 21 are preferably milled into the base 10 by a milling cutter (not shown).

With particular reference to FIG. 4, there is shown in exaggerated form, the manner in which plates 14 initially extend beyond the final desired surface S of the base 10. In the particular embodiment of a base 10 of cylindrical form illustrated in the drawings, the plates 14 initially extend beyond the final desired surface S and in particular have a larger diameter than the final diameter of the base 10. It has been found to be most economical to eliminate close tolerances by sizing the plates 14 larger than necessary and allowing wide positive tolerances, and by sizing the magnets 13 smaller than necessary and allowing wide tolerances. As one of the final steps in the manufacturing operation, the base 10 is turned on a lathe by rotating the base 10 in conventional manner relative to a cutter which moves at a predetermined rate of feed in a direction longitudinally with respect to the base 10, thereby removing material 20 and the portions of the plates 14 radially beyond the final desired surface S of the base 10.

With reference to FIGS. 5-8, there is shown a mold generally indicated at which is useful in performing the molding step of the invention. The mold I 30 is shown to include a pair of 'mold sections 31 and 32 and a pair of end plates 33 and 34. The mold sections 31 and 32 are curved and extend through arcs of about each. The mold section 31 has side edges 31 and 31", and the mold section 32 has side edges 32 and 32". When the mold is assembled side edges 31" and 32" of the respective mold sections 30 and 31 are in liquid-tight abutment with an elongated nozzle 35, and there is a gap between the side edges 31' and 32' as best shown in FIGS. 7 and 8. A plurality of tie rods 36 cause the end plates 33 and 34 to exert clamping pressure on the ends of the mold sections 31 and 32 when nuts 37 are tightened.

Each of the mold sections 31 and 32 has a plurality of positioning and holding grooves 38 formed at its inside surface. These grooves 38 extend in an arcuate direction between the respective side edges 31' and 31" and 32 and 32". Assuming that a circular cylindrical printing base is to be fabricated, a circular cylindrical member 15 shown to take the form of a sleeve is provided. Then plates 14 and magnets 13 can be assembled onto the member 15 either individually or as sets or groups of magnet circuits. In the illustrated embodiment, one magnetic circuit comprises a permanent magnet 13 disposed between and in contact with a pair of plates 14. If the magnetic circuits are to be assembled as sets the attractive force of the magnet 13 will hold the associated magnetizable plates 14 to it and hence each magnetic circuit is easily moved into position by sliding the magnetic circuit onto the member 15. In the illustrated embodiment the magnetic circuits 12 are shown to be spaced apart. As the magnets 13 have a diameter which is intentionally less than the final diameter of the base 10 and the plates 14 having a diameter greater than the final diameter of the base 10, the accuracy of the outer surface of the base 10 is not dependent upon accurate sizing or location of the holes 13 and 14. Accordingly, holes 13' and 14 are acceptable even though larger than necessary by a considerable tolerance.

Endmost grooves 39 in the mold sections 31 and 32 are shown to receive end plates 16. The grooves 38 have a width which is slightly greater than the cornbined thicknesses of two plates 14 and the magnet 13 so that during the molding operation the magnetic circuits 12 are not apt to be displaced by the moldable material. Here again accuracy of positioning the magnetic circuits 12 is not necessary. With the components which are to comprise the base 10 disposed within the mold and the mold in the clamped condition as shown in FIG. 6, the moldable, non-magnetic adhesive material is forced into the mold through orifices 35 in the nozzle 35. As the material enters the mold, air escapes through the gap between side edges 31 and 32' of the mold sections 31 and 32. As the magnets 13 and the associated plates 14 have flat sides, the moldable material does not flow between the contacting surfaces. However, material is able to flow into the spaces between plates 14 of adjacent magnetic circuits 12, into the space around the magnets 13 and between the associated plates 14, between the plates 14 of the endmost magnetic circuits 12 and the end plates 16, into and through holes 18 in the plates 14, and into holes 19 in the end plates 16, thereby providing a unitized base. As the moldable material, preferably in the form of epoxy gradually fills the spaces described above until excess non-magnetic material flows into the gap between side edges 31- and 32 at the time flow of additional material into the mold through the nozzle 35 is interrupted and the moldable material is allowed to set and harden. After the material 20 sets and hardens, the mold 30 is removed with respect to the base. and the base 10 is ready to be turned on a lathe.

lf desired, many of the benefits of this invention can be achieved by applying the invention to a flat bed type of magnetic base. In that eventthe final desired surface of the base 10 can be achieved by ,using a milling cutter (not shown). The milling cutter would make passes relative to the base 10 in the same direction as the direction in which the plate and magnets extend.

It is preferred touse one-piece magnets 13 although segmented magnets can be employed, if desired, within the spirit of the invention. I

Other embodiments and modifications of this invention will suggest themselves to those skilled in the art, and all such of these as come within the spirit of this invention are included within its scope as best defined by the appended claims.

I claim: v

1. Method of making a printing base for mounting a printing plate, comprising the steps of: providing a cylindrical member, placing at least two magnetic circuit means on said cylindrical member, each circuit means including annular magnet means disposed between a pair of annular magnetizable plates, said plates having a greater diameter than said magnet means, placing said cylindrical member with said magnetic circuit means in a mold, flowing non-magnetic moldable material between the plates of adjacent magnetic circuit means, between the plates of each magnetic circuit means around the associated magnet means, and beyond the final desired diameter of the base, and trimming off the portions of all the plates and non-magnetic material beyond to the final desired diameter.

2. Method of making a printing base as defined in claim 1, further comprising the steps of: flowing the moldable non-magnetic material into the mold from the bottom so as to purge air out of the mold as the non-magnetic material fills the mold.

3. Method of making a printing base as defined in claim 1, further comprising the steps of: providing at least one groove in the outer surface of the base to accommodate a leading edge of a printing plate.

4. Method of making a printing base for mounting a printing plate, comprising the steps of: providing a cylindrical member, placing at least one magnetic circuit means on said cylindrical member, a circuit means including annular magnet means disposed between a pair of annular magnetizable plates, said plates having a greater diameter than said magnet means, placing said cylindrical member with said magnetic circuit means in a mold, molding non-magnetic material between said plates and around said magnet means to beyond the final surface of the base, removing the base from the mold, and trimming off the plates and the nonmagnetic moldable material to the desired diameter which is greater than the diameter of said magnet means.

5. Method of making a printing base as defined in claim 4 wherein said step of trimming includes turning the outer surface of said base on a lathe.

6. Method of making a printing base as defined in claim 4, providing at least one hole in each plate, at least a part of each hole extending beyond the surface of said magnet means so that the moldable non magnetic material can flow into said holes and thereby key said plates together.

7. Method of making a magnetic base for mounting a printing plate, comprising the steps of: providing flat magnet means disposed between and in contact with a pair of magnetizable plate means, said magnet means extending short of the final desired surface of the base,

said plate means extending beyond the final desired surface of the base, flowing moldable non-magnetic material between said plate means and around said magnet means to beyond the final surface of the base, and thereafter trimming off the portions of all said plates means and all the material beyond to the final surface.

8. Method of making a magnetic base for mounting a printing plate, as defined in claim 7, further comprising the steps of: providing a hole in each of said plates, at least a part of each hole extending beyond the surface of said magnet means so that the moldable nonmagnetic material can flow into said holes and thereby key said plates together.

9. Method of making a magnetic base for mounting a printing plate, comprising the steps of: providing flat magnet means disposed between a pair of magnetizable plates, providing each of said plate means with a keying means, said magnet means extending short of the final desired surface of the base, said plates extending beyond the final desired surface of the base, keying said plate means together by means of non-magnetic moldable material engageable with said keying means, and thereafter trimming off the portions of all of said plates beyond the final surface.

10. Method of making a magnetic base for mounting a printing plate, comprising the steps of: assembling magnet means and plates ina mold in alternating relationship, providing holes in the plates at locations so that at least a part of each hole is beyond the surface of the associated magnet means, and keying the plates together by flowing moldable non-magnetic material into spaces between the plates and into the holes.

11. Method of making a printing base for mounting a printing plate, comprising the steps of: providing at least two permanent magnetic circuit devices having substantially equal magnetic flux fields at the surface of the base, each magnetic circuit device having permanent magnet means disposed between a pair of magnetizable plates, arranging the magnets such that the plates are alternately poled in a north-south-northsouth pattern, and spacing the magnetic circuit devices apart by a distance such that the strength, at the surface of the base, of the flux field between the next adjacent plates of adjacent magnetic circuit devices is substantially equal to the strength, at the surface of the base, of the flux field between the plates of a magnetic circuit device.

12. Method as defined in claim 11, further comprising the steps of: the plates extending to the surface of the base and the magnets terminating short of the surface of the base, and flowing moldable non-magnetic material into the space between the plates of each magnetic circuit device and into the space between adjacent magnetic circuit devices.

13. A magnetic base for mounting a printing plate, comprising: mounting means, a plurality of magnetic circuit means disposed in spaced apart relationship on said mounting means, each circuit means including an annular magnet, an annular magnetizable plate disposed on each side of and in contact with each magnet, end plates spaced apart from the endmost magnetizable plates, at least one hole in each magnetizable plate extending at least partly beyond the associated magnet, and non-magnetic material disposed:

a. between the magnetizable plates of adjacent magnetic circuit means, b. between the endmost magnetizable plates and the associated end plates,

c. around said magnets, and

d. in said holes, the initial diameter of said magnetizable plates and of said non-magnetic material being greater than the final desired diameter of said base, the initial diameter of said magnets being less than the final desired diameter of said base, the portion of said magnetizable plates and of the non-magnetic material beyond the final desired diameter being removed after assembly of said base.

14. A magnetic base for mounting a printing plate, comprising: at least two permanent magnetic circuit devices having substantially equal magnetic flux fields at the surface of the base, each magnetic circuit device having permanent magnet means disposed between a pair of magnetizable plates, the magnets being alternately poled in a north-south-north-south pattern, said magnetic circuit devices being spaced apart a distance such that the strength, at the surface of the base, of the flux field between next adjacent plates of adjacent magnetic circuit devices is substantially equal to the strength, at the surface of the base, of the flux field between the plates of a magnetic circuit device.

15. A magnetic printing base as defined in claim 14, wherein the plates extend to the surface of the base and the magnets terminate short of the surface of the base,

and moldable non-magnetic material in the space between the plates of each magnetic circuit device and the space between adjacent magnetic circuit devices.

16. Method of making a printing base for mounting a printing plate, comprising the steps of: providing a cylindrical member, placing at least two magnetic circuit means on said cylindrical member, each circuit means including annular magnet means disposed between a pair of annular magnetizable plates, said plates having a greater diameter than said magnet means, providing at least one hole in each plate, placing said cylindrical member with said magnetic circuit means in a mold, flowing non-magnetic moldable material between the plates of adjacent magnetic circuit means, and between the plates of each magnetic circuit. means around the associated magnet means, at least a part of each hole extending beyond the surface of the associated magnet means so that there is flow of the non-magnetic material into and through said holes.

17. A magnetic base for mounting a printing plate, comprising: a pair of magnetizable plate means, magnet means disposed between and in contact with said plate means, keying means disposed below the surface of said base for each of said plate means, and nonmagnetic moldable material disposed between said plate means and around said magnet means and in engagement with said keying means, wherein said keying means includes a hole in each plate means, at least a portion of each of said holes extending beyond the magnet means.

18. A magnetic base as defined in claim 17, wherein each hole extends short of the surface of said base. 

1. Method of making a printing base for mounting a printing plate, comprising the steps of: providing a cylindrical member, placing at least two magnetic circuit means on said cylindrical member, each circuit means including annular magnet means disposed between a pair of annular magnetizable plates, said plates having a greater diameter than said magnet means, placing said cylindrical member with said magnetic circuit means in a mold, flowing non-magnetic moldable material between the plates of adjacent magnetic circuit means, between the plates of each magnetic circuit means around the associated magnet means, and beyond the final desired diameter of the base, and trimming off the portions of all the plates and non-magnetic material beyond to the final desired diameter.
 2. Method of making a printing base as defined in claim 1, further comprising the steps of: flowing the moldable non-magnetic material into the mold from the bottom so as to purge air out of the mold as the non-magnetic material fills the mold.
 3. Method of making a printing base as defined in claim 1, further comprising the steps of: providing at least one groove in the outer surface of the base to accommodate a leading edge of a printing plate.
 4. Method of making a printing base for mounting a printing plate, comprising the steps of: providing a cylindrical member, placing at least one magnetic circuit means on said cylindrical member, a circuit means including annular magnet means disposed between a pair of annular magnetizable plates, said plates having a greater diameter than said magnet means, placing said cylindrical member with said magnetic circuit means in a mold, molding non-magnetic material between said plates and around said magnet means to beyond the final surface of the base, removing the base from the mold, and trimming off the plates and the non-magnetic moldable material to the desired diameter which is greater than the diameter of said magnet means.
 5. Method of making a printing base as defined in claim 4 wherein said step of trimming includes turning the outer surface of said base on a lathe.
 6. Method of making a printing base as defined in claim 4, providing at least one hole in each plate, at least a part of each hole extending beyond the surface of said magnet means so that the moldable non-magnetic material can flow into said holes and thereby key said plates together.
 7. Method of making a magnetic base for mounting a printing plate, comprising the steps of: providing flat magnet means disposed between and in contact with a pair of magnetizable plate means, said magnet means extending short of the final desired surface of the base, said plate means extending beyond the final desired surface of the base, flowing moldable non-magnetic material between said plate means and around said magnet means to beyond the final surface of the base, and thereafter trimming off the portions of all said plates means and all the material beyond to the final surface.
 8. Method of making a magneTic base for mounting a printing plate, as defined in claim 7, further comprising the steps of: providing a hole in each of said plates, at least a part of each hole extending beyond the surface of said magnet means so that the moldable non-magnetic material can flow into said holes and thereby key said plates together.
 9. Method of making a magnetic base for mounting a printing plate, comprising the steps of: providing flat magnet means disposed between a pair of magnetizable plates, providing each of said plate means with a keying means, said magnet means extending short of the final desired surface of the base, said plates extending beyond the final desired surface of the base, keying said plate means together by means of non-magnetic moldable material engageable with said keying means, and thereafter trimming off the portions of all of said plates beyond the final surface.
 10. Method of making a magnetic base for mounting a printing plate, comprising the steps of: assembling magnet means and plates in a mold in alternating relationship, providing holes in the plates at locations so that at least a part of each hole is beyond the surface of the associated magnet means, and keying the plates together by flowing moldable non-magnetic material into spaces between the plates and into the holes.
 11. Method of making a printing base for mounting a printing plate, comprising the steps of: providing at least two permanent magnetic circuit devices having substantially equal magnetic flux fields at the surface of the base, each magnetic circuit device having permanent magnet means disposed between a pair of magnetizable plates, arranging the magnets such that the plates are alternately poled in a north-south-north-south pattern, and spacing the magnetic circuit devices apart by a distance such that the strength, at the surface of the base, of the flux field between the next adjacent plates of adjacent magnetic circuit devices is substantially equal to the strength, at the surface of the base, of the flux field between the plates of a magnetic circuit device.
 12. Method as defined in claim 11, further comprising the steps of: the plates extending to the surface of the base and the magnets terminating short of the surface of the base, and flowing moldable non-magnetic material into the space between the plates of each magnetic circuit device and into the space between adjacent magnetic circuit devices.
 13. A magnetic base for mounting a printing plate, comprising: mounting means, a plurality of magnetic circuit means disposed in spaced apart relationship on said mounting means, each circuit means including an annular magnet, an annular magnetizable plate disposed on each side of and in contact with each magnet, end plates spaced apart from the endmost magnetizable plates, at least one hole in each magnetizable plate extending at least partly beyond the associated magnet, and non-magnetic material disposed: a. between the magnetizable plates of adjacent magnetic circuit means, b. between the endmost magnetizable plates and the associated end plates, c. around said magnets, and d. in said holes, the initial diameter of said magnetizable plates and of said non-magnetic material being greater than the final desired diameter of said base, the initial diameter of said magnets being less than the final desired diameter of said base, the portion of said magnetizable plates and of the non-magnetic material beyond the final desired diameter being removed after assembly of said base.
 14. A magnetic base for mounting a printing plate, comprising: at least two permanent magnetic circuit devices having substantially equal magnetic flux fields at the surface of the base, each magnetic circuit device having permanent magnet means disposed between a pair of magnetizable plates, the magnets being alternately poled in a north-south-north-south pattern, said magnetic circuit devices being spaced apart a distance such that the strength, at the surfAce of the base, of the flux field between next adjacent plates of adjacent magnetic circuit devices is substantially equal to the strength, at the surface of the base, of the flux field between the plates of a magnetic circuit device.
 15. A magnetic printing base as defined in claim 14, wherein the plates extend to the surface of the base and the magnets terminate short of the surface of the base, and moldable non-magnetic material in the space between the plates of each magnetic circuit device and the space between adjacent magnetic circuit devices.
 16. Method of making a printing base for mounting a printing plate, comprising the steps of: providing a cylindrical member, placing at least two magnetic circuit means on said cylindrical member, each circuit means including annular magnet means disposed between a pair of annular magnetizable plates, said plates having a greater diameter than said magnet means, providing at least one hole in each plate, placing said cylindrical member with said magnetic circuit means in a mold, flowing non-magnetic moldable material between the plates of adjacent magnetic circuit means, and between the plates of each magnetic circuit means around the associated magnet means, at least a part of each hole extending beyond the surface of the associated magnet means so that there is flow of the non-magnetic material into and through said holes.
 17. A magnetic base for mounting a printing plate, comprising: a pair of magnetizable plate means, magnet means disposed between and in contact with said plate means, keying means disposed below the surface of said base for each of said plate means, and non-magnetic moldable material disposed between said plate means and around said magnet means and in engagement with said keying means, wherein said keying means includes a hole in each plate means, at least a portion of each of said holes extending beyond the magnet means.
 18. A magnetic base as defined in claim 17, wherein each hole extends short of the surface of said base. 